1 Field of the Invention
The invention relates generally to a material for filling a dental root canal and a method for preparing same. Specifically, the invention relates to a compounded thermosplasticized, injectable resin for filling a dental root canal, and a method of making same.
2 Description of the Prior Art
Materials presently known for filling a dental root canal include pastes, gutta percha cones, and thermosplasticized gutta percha.
Pastes consist generally of materials in the calcium hydroxide series, used by filling the root canal therewith. Such pastes, however, are generally difficult and inconvenient to use, and are therefore not desirable for use in dental root canal filling.
Gutta percha cones are the most widely used dental root canal filling material. They consist of thin, solid rods of gutta percha, a purified, coagulated, milky exude of various trees. In rod form, however, it is very difficult to use gutta percha to make a complete seal to the tip of the root canal because the length and size of the root canal is different for each patient. For example, molars with curved root canals require advanced and different techniques for inserting gutta percha cones up to the root canal tip, even after root canal enlargement.
In preparing a dental root canal for filling with a material such as gutta percha, the tooth pulp is first extirpated from the tooth. The length of the root canal is then measured, up to the clinical apical foramen, by a meter, or by a compensated measurement directly from an X-ray. An insertion needle known as a reamer is then used to enlarge the root canal, and a dental file is then used to form an apical seat approximately 1 to 2 millimeters inside the apical foramen. The shaped root canal is then cleansed and sterilized.
In filling the dental root canal, prepared as described above, by using gutta percha cones, a gutta percha cone of a size larger than the last dental file used to form the apical seat, is pressed laterally to the root canal wall by an instrument known as a spreader, making room for several further gutta percha cones which are then inserted for packing. After treatment, X-rays are taken to determine whether the root canal is packed.
However, after filling the dental root cannal by using gutta percha cones, patients frequently complain of pain, indicating improper healing and filling, although the X-rays had indicated complete packing. This problem is caused in part by imperfect packing of the the root canal, resulting from floating of the main gutta percha cone from the apical foramen, and from imprecise shaping of the root canal. In shaping the root canal by filling, the shape formed thereby does not precisely coincide with the shape of the gutta percha cones, whereby dead space areas are formed, which becomes sources of secondary infections. Further, due to lateral pressures exerted after filling, the gutta percha cones frequently become separated from the foramen apex.
Gutta percha cones are also used in heated form in several root canal filling methods.
In a root canal filling method known as the lateral condensation method, hard gutta percha is inserted and melted at the top of the tooth downward toward the tip, causing lateral flow and softening. However, the gutta percha must be heated to a relatively high temperature to flow freely, and must further be removed, reheated, and reinserted, which, aside from causing discomfort, and lengthy treatment, further causes rapid cooling. Coupled with the syringe pressurization, this method frequently results in fracturing of the filling and the tooth. Further, gutta percha is also absorbed in the root canal, and prevented from being absorbed in the surrounding tissues, when pushed out of the apex hole, causing harmful side effects.
It has been considered that heat could be applied to gutta percha cones for use in a root canal filling method known as the vertical condensation method. However, since gutta percha cones were developed for use in the lateral condensation method, they contain natural rubber and resin, to maintain lateral strength, which have a relatively high plasticity temperature, in the range of 80.degree. C. to 90.degree. C., which operating temperature would give a patient considerable pain, or break a filling or tooth by exerting excessive vertical pressure due to rapid cooling of the material.
Thermoplasticized gutta percha has been developed relatively recently, and is injectable in heated form to mold to the prepared root canal.
In using thermoplasticized gutta percha, it is heated to a temperature sufficiently high to render it sufficiently plasticized, then injected by syringe into the prepared dental root canal which it fills under pressure, and is then permitted to cool and harden.
One presently known form of thermoplasticized gutta percha consists of gutta percha cones to which a thermoplasticizing agent has been added. This form has been described generally in an article by Dr. Fulton S. Yee et. al., "Three-Dimensional Obturation of the Root Canal using Injection-Molded, Thermoplasticized Dental Gutta-Percha", 3 Journal of Endodontics, No. 5, pages 168-174 (May 1977). The thermoplasticized gutta percha material described generally therein, however, must be heated to a temperature of 160.degree. C. to generate unrestrained flow for use as an injectable filling, which temperature is too high for manual handling and use on patients in clinical situations.
The other presently known form of thermoplasticized gutta percha consists of gutta percha resin, compounded with other materials to plasticize at a temperature in the range of 50.degree. C. to 70.degree. C., which has been described in Japanese patent application serial No. 51-111602, filed Sept. 17, 1976, for "A Dental Material for Root Canal Filling which is Filled by Means of a Syringe", By Toyo Chemical laboratories, Inc., Tokyo, Japan. However, the thermoplasticized gutta percha material described therein is not of optimum efficiency and convenience, in that it is gutta percha based, and must be heated to a temperature not optimallly suited for routine clinical use by technicians.